Drop the fallback to directly processing YAML files in loading exception codes if there is no resolved codes file.

[AliAlaa88]

Describe the bug
Fallback to directly processing YAML files in loading exception codes if there is no resolved codes file produces invalid code.

To Reproduce
Steps to reproduce the behavior:

1. On Branch 'Ali/Sverilog'
2. Remove the --resolved-codes from the sh in the sverilog task in the Tasks.rake file
3. Run do gen:sverilog

Text output/Error Messages
This is an example of output error in the generated .svh

  localparam logic [5:0] CAUSE_ENVIRONMENT_CALL_FROM_<%__IF_EXT?(:H)__%>V<%__END__%>U_MODE = 6'h08;
  localparam logic [5:0] CAUSE_ENVIRONMENT_CALL_FROM_<%__IF_EXT?(:H)__%>H<%__END__%>S_MODE = 6'h09;

[ThinkOpenly]

Per @jordancarlin (#1090 (comment)):

we should drop the fallback to directly processing YAML files. It produces invalid code (which is why the other version was added in the first place), so it would be better to just throw an error or skip the exception cause section. As is it makes the entire generated artifact unusable if it reaches this code.